1. Field of the Invention
The present invention relates to a method of bonding, by resistance heating through energization while applying pressure in an axial direction, a first metallic member including an opening and a second metallic member including an outer circumferential wall section capable of coming into partial contact with an inner circumferential wall section of the first metallic member that surrounds the opening, and the like.
2. Description of the Background Art
Conventionally, a bonding method described in Japanese Patent Application Laid-open No. 2004-17048 is known as a type of so-called ring mash welding method. Specifically, the method described in Japanese Patent Application Laid-open No. 2004-17048 is arranged so as to overlap a hollow first metallic member and a second metallic member whose outer diameter is slightly greater than an inner diameter of the first metallic member in an axial direction, and to join an inner circumferential surface of the first metallic member to an outer circumferential surface of the second metallic member by supplying a welding current while applying a pressurizing force in the axial direction.
In this case, a junction of the first metallic member and the second metallic member takes the form of a diffusion bonding instead of a fusion bonding. In other words, by energization while applying a pressurizing force on both of the metallic members, the metals at contact portions are softened and a plastic flow is generated to metallurgically join newly-formed surfaces of the metals.
A ring mash bonding method such as that described in Japanese Patent Application Laid-open No. 2004-17048 is advantageous compared to general fusion bonding such as arc welding in that segregation of carbides due to fusion, solidification cracking due to the effect of heat, and the like do not occur and that only a short period of time is required for welding.
However, with the method disclosed in Japanese Patent Application Laid-open No. 2004-17048, when, for instance, a junction area of the first metallic member and the second metallic member is enlarged for the purpose of increasing joint strength, a problem arises in that the pressurizing force and a current value must be increased accordingly, resulting in greater facility size. Therefore, there is a need to improve joint strength while minimizing the energy required for the bonding.